This invention relates to dust control equipment and, more particularly, to a cylindrical baghouse equipped with a rotor cleaning head to isolate and clean filter bags.
Continuous emphasis on environmental quality has resulted in increasingly strenuous regulatory controls on industrial emissions. One technique which has proven highly efficient in controlling air pollution has been the separation of undesirable particulate matter from a gas stream by fabric filtration.
Such filtration is carried out in dust collection equipment known in the trade as a "baghouse" which operates on the same general principle as an ordinary household vacuum cleaner, except on a much larger scale. Basically, the baghouse includes a sheet metal housing divided into two chambers, referring to as plenums, by a tube sheet having a plurality of vertically arranged fabric tubes or bags. A particle-laden gas stream, induced by the action of a fan, flows into the dirty air plenum wherein dust accumulates on the cloth bag as the bag passes through the fabric into the clean air plenum and out the exhaust. Continuous operation of the unit causes a cake of dust to build up on the bags which, unless removed, will reduce and eventually stop the flow of gas through the filters. Cleaning may be accomplished by backflushing the filters with cleaning air, thereby dislodging the dust cake from the bags to fall to the bottom of the dirty air plenum for subsequent removal.
Baghouses to which this invention particularly relates are cylindrical in shape with a cone shaped lower section for collection of the dust cake. These baghouses are normally characterized in the industry as small or bag houses, as opposed to larger versions which are usually rectangularly shaped with a lower hopper section for collection of the dust cake.
In the cylindrical type baghouse, the bags are arranged in concentric rings successively outwardly from the longitudinal axis of the baghouse. Cleaning is achieved by a rotating sweep arm centrally pivoted within the clean air plenum to rotate over the tube sheet. Blow back air, delivered along the length of the sweep arm, simultaneously backflushes the bags lying on a common radial from the center of the tube sheet. This cleaning technique necessarily limits the size and capacity of the baghouse since the bags in the outer rings must be aligned on a radial from the longitudinal axis of the baghouse with the bags forming the interior rings. In other words, the space between adjacent bags in each successive outer ring gets increasingly larger. If such spaces are used to accommodate additional filter bags, such bags can not lie on a radial with any bags forming the inner rings and, therefore, it is necessary to provide a sweep arm with multiple cleaning heads in order to clean bags having various geometric arrangements on the tube sheet.
Both of the foregoing two alternative approaches to geometric layout of the filter bags, with their attendant cleaning mechanisms, are commercially available. In one type of unit, the filters are aligned on common radials from the center of the bagouse and an air blow back manifold rotates 360.degree. around the central axis of the baghouse to sweep the tube sheet area. Cleaning air is provided the full length of the manifold in order to clean simultaneously the full radius of the tube sheet so that all bags are cleaned with each complete revolution of the sweep arm. The amount of blow back air required by this arrangement must therefore be sufficient to clean at one time all on a common radial along the entire length of the sweep arm. As previously mentioned, however, such geometric spacing of bags does not effectively utilize the space between adjacent filters in the outermost concentric ring of bags.
An alternative commercial unnit arranges bags in the outermost concentric rings to more effectively utilize this area, but such bags do not lie on common radials with the filter bags in the inner rings of bags. This being the case, therefore, it is necessary to provide one cleaning head to clean the inner several rings of bags with one geometric layout and a second cleaning head to clean the outermost rings of bags with a different geometric layout. The cleaning system itself must have sufficient capacity to provide cleaning air to multiple numbers of bags at the same time.
There remains a need for a cylindrical baghouse effectively utilizing the amount of tube sheet area available for filters and for a system to efficiently and economically clean such filters. The primary goal of the present invention is to meet this need.
More specifically, an object of the invention is to provide a cylindrical filter unit wherein the filter bags may be arranged in concentric rings about the center of the tube sheet without the constraint of aligning the filters on common radials. In this fashion, filters in the outermost rings can be arranged sufficiently close together to achieve the maximum number of filters without regard to alignment of the filters with any filters forming the interior rings. Thus, the entire surface area of the tube sheet is available for use in arranging filter bags to maximize the filtering capacity of the unit.
Another object of the invention is to provide a cylindrical baghouse wherein the filter bags are cleaned one at a time in order to maximize cleaning efficiency. As a corollary hereof, significant economies are achieved in sizing the cleaning system to clean one bag at a time, as opposed to multiple bag cleaning systems.
An additional object of the invention is to provide a cylindrical baghouse of the character described wherein a cleaning manifold is pivotally mounted to rotatably sweep the surface of the tube sheet. The manifold is equipped with a valving mechanism to deliver blow back air to only one of the concentric rings of filters during one complete revolution of the sweep arm in order to clean, one at a time, the filter bags comprising that particular concentric ring of filters. Additionally, the valve mechanism is controlled by cam means to cause a subsequent concentric ring of bags to be cleaned with each successive full revolution of the sweep arm.
A further object of the invention is to provide a cylindrical baghouse of the character described which is rugged and durable in construction and economical in manufacture. Reliability and ease of maintenance are also significant features of this unit.
Yet another object of the invention is to provide a baghouse of the character described particularly adapted to the use of low pressure cleaning air. The sweep arm effectively seals against each filter mouth, one at a time, to dislodge dust cake with low pressure air in a highly efficient manner.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description of the drawings.